This invention relates generally to a jackscrew apparatus for actuating a mechanism operably connected to a nut portion of the jackscrew.
Jackscrews are commonly used to actuate mechanisms such as vehicle door latch components and to move other members that, to be moved efficiently, require the mechanical advantage provided by such a system. A typical jackscrew includes a nut that is supported for reciprocal translational motion and against rotational motion. A screw threadedly and drivingly engages the nut to drive the nut in a driven direction along the screw. The nut may be backdriven, i.e., returned to a home position on the screw, by reversing screw rotation.
It""s known for jackscrews to include self-backdriving features that either backdrive or assist in backdriving or moving a jackscrew nut opposite the driven direction to a home position. To accomplish this, it""s known for a self-backdriving jackscrew system to include a spring that""s connected between the jackscrew nut and a stationary structure spaced from the nut in the driven direction. In this position, the spring bears on the nut, resisting nut motion in the driven direction. As the nut moves closer to a distal end of the screw in the driven direction, the spring builds up backdriving force. When driving force is removed from the screw, the pent-up backdriving force of the spring pushes axially on the screw, either causing the nut to return to its home position or aiding a reversible drive motor in returning the nut to its home position.
To function properly, self-backdriving jackscrew systems of this type must have jackscrew nut threads and screw threads of a relatively high pitch, a relatively stiff backdriving spring, and/or a suitable lubricant between the threads of the nut and screw. On their own, or in combination, incorporation of highly pitched threads and a relatively stiff backdriving spring necessitate the selection of a more powerful drive motor than would otherwise be required to operate the jackscrew for a given amount of resistance provided by the member intended to be moved by the jackscrew.
It would be desirable, therefore, to provide a jackscrew apparatus comprising a backdriving system that provides less resistance to the movement of a jackscrew nut in the driving direction. It would also be desirable for such an apparatus to include a backdriving system that backdrives its jackscrew nut more efficiently and with fewer frictional losses.
The invention is a self-backdriving jackscrew apparatus for returning or reducing resistance to the return of a jackscrew nut to a home position on a jackscrew shaft. The apparatus includes a nut supported for reciprocal translational motion and against rotational motion and having internal helical threads. The apparatus also includes a screw having external helical threads that complement and threadedly engage those of the nut. The screw is supported for rotation about a longitudinal screw axis to drive the nut in a driven direction along the longitudinal screw axis when the screw is rotated in one direction about the screw axis and to backdrive the nut opposite the driven direction when the screw is rotated about the screw axis in a second rotational direction opposite the first rotational direction. A biasing member is connected to the screw and is configured to exert backdriving force on the screw that turns the screw in the second rotational direction about the screw axis.
Therefore, because the biasing member applies backdriving force to the screw rather than axially-directed force to the nut, the biasing member is able to backdrive or assist in backdriving the nut more efficiently and with fewer frictional losses.
The invention also includes a method for returning or reducing resistance to the return of a jackscrew nut to a home position on a jackscrew shaft. According to this method a nut having internal helical threads is supported for reciprocal translational motion and against rotational motion on a screw having external helical threads complementing and threadedly engaging those of the nut. The nut is supported on the screw for rotation in a first rotational direction about a longitudinal screw axis to drive the nut in a driven direction along the longitudinal screw axis when the screw is rotated in one direction about the screw axis and to backdrive the nut opposite the driven direction when the screw is rotated about the screw axis in a second rotational direction opposite the first rotational direction. A biasing member is connected to the screw and is configured to provide backdriving force to rotate the screw in the second rotational direction. The nut is then moved along the screw in the driven direction against the backdriving force of the biasing member by rotating the screw in a first rotational direction. The nut is then released and the backdriving force of the biasing member is allowed to move the nut along the screw opposite the driven direction by causing the nut to rotate in the second rotational direction.